Battery-powered devices (e.g., consumer electronic devices, electric and hybrid automobiles, etc.) are charged from a power source (e.g., AC power outlet) through a charging device. The charging device couples the battery to the power source through an adaptor. The cord extending between the power source and the battery-powered device can take up space. In situations where multiple devices require charging, each with their own charger and cord, the charging area can become cramped and inconvenient.
Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device. Wireless power transmission using inductive coil is one method considered as an untethered method for transferring power wirelessly through a coupled electromagnetic field. In inductive wireless power transmission, power is transferred by transmitting an electromagnetic field through a transmit coil. On the receiver side, a receiver coil may couple with the transmit coil through the electromagnetic field, thus receiving the transmitted power wirelessly. The distance between the transmitter and receiver coils at which efficient energy transfer can take place is a function of a coupling coefficient between the coils. The coupling efficiency may be significantly improved if the coils are sized and operated at such a frequency that they are physically within the so-called “near-field zone” of each other.
During power transfer from the transmitter to the receiver, data may be communicated between the transmitter and the receiver. Conventional methods of communication include one-way communication via a communication link from the receiver to the transmitter that is based on backscatter modulation in which the load is modulated on the receiver side. As a result, using conventional methods, only the receiver has the ability to send data to the transmitter. Other conventional methods that achieve two-way communication include separate RF coils, which require additional components that may increase cost, area, and complexity.